In order to add new user to the interface you need to be an Admin or Super Admin user.
If you can't see User Management in the dropdown then you are not an Admin user (highlight 2.)
Click on the face icon in the top right hand side of the interface to bring up the drop down menu.
Click on User Management in the dropdown men
Click on Create User which will then give you the list to fill out.
User name and email address should match for notifications.
Once you have filled out all the boxes/drop down selections just click "Create New User".
If you need to edit any user then click on edit user instead of create user.